Scope and purpose

Fixes #2373. Another PR intends to add documentation and release notes.

This pull request

• Adds DHCP stats graphs to VLAN and Prefix pages in NAV where recent-enough stats for that VLAN/Prefix are found in the Carbon/Graphite database:
  

Contributor Checklist

Every pull request should have this checklist filled out, no matter how small it is.
More information about contributing to NAV can be found in the
Hacker's guide to NAV.

• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation see Add documentation for DHCP stats #3785
• Linted/formatted the code with ruff, easiest by using pre-commit
• Wrote the commit message so that the first line continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/
• Based this pull request on the correct upstream branch: For a patch/bugfix affecting the latest stable version, it should be based on that version's branch (<major>.<minor>.x). For a new feature or other additions, it should be based on master.
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done TODO: add a new issue for using Rickshaw graphs instead of PNG images in graph navlets
• If it's not obvious from a linked issue, describe how to interact with NAV in order for a reviewer to observe the effects of this change first-hand (commands, URLs, UI interactions) See screencast below
• If this results in changes in the UI: Added screenshots of the before and after
• If this adds a new Python source code file: Added the boilerplate header to that file

Testing It For Yourself

You can use the script below to fill the prefixes 192.0.0.0/24, 192.0.1.0/24, 192.0.0.0/26, and ::2:0:0/96 with DHCP stats (you might need to install socat and gawk, and you might need to change 127.0.0.1 to the address of your Carbon/Graphite database):

#!/bin/sh

cat <<EOF |
4 example-1 admin 192.0.0.1 192.0.0.127 127 127 0 100000
4 example-1 admin 192.0.0.129 192.0.0.255 127 127 0 100000
4 example-1 admin 192.0.1.1 192.0.1.255 255 255 0 100000

4 example-1 guest 192.0.2.0 192.0.2.255 256 256 0 10000
4 example-1 guest 192.0.2.0 192.0.2.127 128 128 10001 50000
4 example-1 guest 192.0.2.128 192.0.2.191 64 64 10001 50000
4 example-1 guest 192.0.2.192 192.0.2.255 64 64 10001 50000

6 example-1 admin 0:0:0:0:0:2:0:0 0:0:0:0:0:2:ffff:ffff 4294967296 100 0 100000
6 example-1 guest 0:0:0:0:0:2:0:0 0:0:0:0:0:2:ffff:ffff 4294967296 100 0 100000
EOF

gawk '
BEGIN {
  NOW = systime()
  srand(11)
  INTERVAL = 300
  DAYS = 30
}

NF == 9 {
  a = rand()
  b = rand()
  c = rand()
  _ = 1 / (a + b + c)
  a = a * _
  b = b * _
  c = c * _
  d = rand()*3.14*2
  e = 20 + rand()*8
  f = rand()

  ip_version = $1
  server_name = $2
  group_name = $3
  first_ip = $4; gsub(/[.:]/, "_", first_ip)
  last_ip = $5; gsub(/[.:]/, "_", last_ip)
  total_ips = $6
  upper_limit = $7
  start_offset = $8 * INTERVAL
  end_offset = $9 * INTERVAL
  noise = rand()
  for (offset = start_offset; offset < end_offset; offset += INTERVAL) {
    sine = (sin((offset*3.14*2)/(3600*e) + d)+1)/2
    noise = noise*f + rand()*(1-f)
    assigned_ips = int(sine*upper_limit*a+upper_limit*b+noise*upper_limit*c)
    printf("nav.dhcp.servers.%s.range.custom_groups.%s.%d.%s.%s.unassigned %d %d\n", server_name, group_name, ip_version, first_ip, last_ip, total_ips - assigned_ips, NOW - offset)
    printf("nav.dhcp.servers.%s.range.custom_groups.%s.%d.%s.%s.assigned %d %d\n", server_name, group_name, ip_version, first_ip, last_ip, assigned_ips, NOW - offset)
    printf("nav.dhcp.servers.%s.range.custom_groups.%s.%d.%s.%s.total %d %d\n", server_name, group_name, ip_version, first_ip, last_ip, total_ips, NOW - offset)
  }
}' |

socat - tcp:127.0.0.1:2003

Here's a screencast (which, after the most recent changes, is a bit outdated, but still representative):

At 2:00 in the video, notice that the graph labelled DHCP ranges in 'guest' on server 'kea-trd' has stats from ranges in both 192.0.2.0/24 and 198.51.100.0/24 despite vlan 20 only containing 192.0.2.0/24. This is because whenever a group (here: 'guest' on server 'kea-trd') has at least one range/pool/subnet overlapping with the VLAN/Prefix, the whole group will be displayed on that VLAN/Prefix's page.